On Thursday Sri Lanka's Supreme Court ruled that Sirisena's decision to dissolve parliament before the end of its term was unconstitutional, a judgement that eventually led to the return of Wickremesinghe as prime minister
Three lawmakers from Sri Lankan President Maithripala Sirisena's party defected to the government of Prime Minister Ranil Wickremesinghe on Tuesday after a dispute between the two leaders.
The island nation was plunged into crisis in October after Sirisena replaced Wickremesinghe with ex-president Mahinda Rajapaksa, without the backing of parliament, leading to protests and downgrades of Sri Lanka's debt.
Rajapaksa, best known for crushing a long-running insurgency in the north of the country and drawing Sri Lanka closer to China, failed to win a parliamentary majority and resigned on Saturday as a government shutdown loomed.
Wickremesinghe was then sworn in as prime minister for the fifth time in a remarkable comeback.
"We joined the government... as the party and the country has been dragged into a difficult position,” Vijith Wijayamuni Soysa, one of the three lawmakers told parliament.
With the latest defections, Wickremesinghe has the backing of 120 legislators in the 225-member parliament.
Sirisena told a party gathering later on Tuesday that he would not allow any defector to be sworn in as a minister in Wickremesinghe's cabinet, which is yet to be appointed.
On Thursday Sri Lanka's Supreme Court ruled that Sirisena's decision to dissolve parliament before the end of its term was unconstitutional, a judgement that eventually led to the return of Wickremesinghe as prime minister.
Members of his ruling United National Party and at least six opposition MPs want to oust Sirisena through an impeachment, though that needs a two-thirds majority in parliament.